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So I have this idea for a gun; it's a normal gun, but it has an underbarrel attachment that fires a harpoon. Normally, the harpoon can be used just as a bayonet, but it has the added benefit of being fire-able. The harpoon can be attached to a rope if desired, or just fired and forgotten.

What I'm wondering is if the harpoon can pierce modern body armor. How fast would it have to be going, what kinds of forces would it take, and how big/powerful would the resulting firing mechanism have to be?

I'd like the harpoon to be re-fireable, so anything that can fire it multiple times would be preferable. Also, I'd like the firing mechanism to be sort of small, at least small enough to be carried by a normal human. The gun need not be pneumatic, nor does it need to resemble an actual harpoon gun, so long as the projectile is vaguely reminiscent of a harpoon (a long metal rod with a pointy bit at the end).

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    $\begingroup$ What would be the point? $\endgroup$ – o0'. Aug 17 '15 at 14:00
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    $\begingroup$ @Lohoris point would be very sharp, i assume! (Sorry. I just could not let this one go by...) $\endgroup$ – Burki Aug 17 '15 at 14:00
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    $\begingroup$ Doesn't work this way, sorry. If you have no answer to why would I want to use such a weapon, then there's no way to answer to any question about that. Either you provide something that makes sense, or there's just no point and make up random stuff anyway. $\endgroup$ – o0'. Aug 17 '15 at 14:10
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    $\begingroup$ A harpoon point would not make a good bayonet. Once it's stuck in, it's difficult to get out. A blade that you could repeatedly stab with is much more useful for defending yourself with. $\endgroup$ – Dave Halsall Aug 17 '15 at 14:47
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    $\begingroup$ You have literally just described a spear launcher. I'd probably actually answer the question if you provided more information, such as: type of body armor, maximum/minimum sizes of projectile, type of gun, etc. $\endgroup$ – Aify Aug 17 '15 at 17:19
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As I understand it, you can pierce a bullet proof vest; like what the police wear; with a knife. There is a different kind of armour that some security guards wear that is designed to stop blades but not bullets. So I think that a harpoon gun might plausibly be fairly effective at piercing some kinds of armour if it is specifically designed for this purpose and is not just an off-the-shelf fishing tool.

Having said that, I do NOT think that the weapon that you just described would be any more effective against an armoured target than say, spraying the sh*t out of them with a sub-machine gun. I mean, think about it; you have to carry around a compressed gass canister, and you only get one shot. If your aim is slightly off and you hit them in the leg, then you just wasted your shot, because you could have just shot them in the legs with a burst of bullets anyway.

So what would be the point?

p.s. Also, bowlturner is incorrect in saying even if the armour is not pierced, that the blunt force would still be lethal. The kickback on the gun would be equal to the force of the projectile. Therefore, the force of the weapon must never exceed what the shooter is prepared to absorb into his own hands and shoulder.

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First problem, it depends on the body armor. The National Institute of Justice (NIJ) has specs for 6 levels of body armor at this time. Level I is for small rounds like a .22 or the .380. Level IV is for protection against armor piercing rifles. The harpoon could easily be subsonic for level I and likely level IIa because of the mass of the harpoon. When you get to level IV I doubt you are going to be piercing the armor with it and it still being a hand held weapon. however a harpoon that could pierce level IIa armor would likely still have enough inertia that you are going to knock down and severely hurt those in the armor. Body armors primary job is to prevent the body from being pierced, to do so it spreads the force of the impact over a larger area, but you hit someone in body armor with a wrecking ball and they are still going to be a pile of mush inside that armor. If the harpoon dents it or applies enough kinetic force the wearer is going down for the count, even if they are still alive.

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  • $\begingroup$ With your wrecking ball analogy, you have not taken into account, "equal and opposite reaction." Whatever blunt force the target is taking into their chest, the shooter is taking that same force into their hands and/or shoulder. If the target sustains broken ribs then the shooter just snapped their thumb and broke their collar bone. $\endgroup$ – Lorry Laurence mcLarry Aug 18 '15 at 2:38
  • $\begingroup$ Its actually even more complicated than that. Most level 1 vests would not stop a subsonic harpoon, as the expectation is for a rifled blunt bullet, instead of a smooth bore knife-like blade. Kevlar, which is often used in body armor, would be defeated easily by a blade. $\endgroup$ – Aron Aug 18 '15 at 3:57

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